The government shutdown has cut into efforts to enforce economic and trade sanctions against Iran and Syria, an official said.

A Treasure Department official told ABC News that the shutdown had “massively reduced staffing” in the Office of Foreign Assets Control, which oversees the enforcement of the sanctions.

The official said employees essential to national security remained on the job, but they represented a “skeleton crew” responsible for protecting the integrity of the U.S. financial system and disrupting the finances of American adversaries.

That includes efforts to combat money laundering and other illicit financing, the official said.

The official said the reduced staff was “unable to sustain its core functions,” including issuing new sanctions against groups helping to fund Iran, Syria and terrorist organizations and issuing licenses to authorize humanitarian activities that might be barred under the sanctions.

Government employees whose jobs relate to the safety of life or property, including much of the Department of Homeland Security, have been exempted from the furloughs.

The White House has not released details about how the shutdown would affect the CIA and NSA.